-
Atari Running on Any Machine:
ARAnyM (Atari Running on Any
Machine) is a virtual machine that can run 32-bit
emulation of Atari ST, TT030 and Falcon including TOS,
FreeMiNT, MagiC and applications for M68k microprocessor
and Graphical Environment Manager (GEM).
-
BOS:
BOS is an x86 32-bit OS
made "with DOS in
mind... with native support for CD-ROM/BURNER, DVD, USB,
most filesystems, up to 4gb of memory... for all those
people that miss the days of DOS programming" (May 2012) written
in assembler by Christoffer Bubach. It is marketed as a
modern alternative to DOS
although it has more of a Unix feel
and functionality although limited to twelve (12)
commands. The current version 0.04 was released in 2005
with no clear date for a 0.05 release if any at all. By
the way, although I have not found what BOS stands for
anywhere in the BOS website, something tells me that it
stands for Bubach Operating System since Bubach
is the name of the creator of the OS.

-
brickOS:
brickOS
(formerly legOS) is an alternative (replacement) OS for
the LEGO Mindstorms RCX Controller.
-
Collapse OS:
Collapse OS is a
"collection of tools and documentation with a
single purpose: preserve the ability to program
microcontrollers through civilizational
collapse" (Jun. 2020) written in Forth in a POSIX
environment. The OS can run with minimal system
requirements — for example, the 3.5 MHz Z80 chip in
Sinclair ZX Spectrum (1982), the 2 MHz Z80A chip in TRS-80 Model III (1980) and the
4 MHz Z80A chip in TRS-80 Model 4 (1983), but no BASIC as originally shipped with these
machines, in favor of much older programming languages as
Forth and assembler (asm). Collapse OS uses a
file system that "contains everything that a
post-collapse computer would manage, that is, all Forth
and assembler source code for the tools it needs to
fulfill its goals" named blk.fs (Sourcehut, Jun. 2020). The
whole idea as explained by the developers is to be able to
run computer systems to rebuild the computer-based
civilization that we are used to even if this means no
GUI. It sounds exciting and an imperative need to learn in
case civilization does collapse, but I had not yet had the
opportunity to play with this OS.
-
DexOS:
DexOS is an open source x86 32-bit OS
written in assembler by Craig Bamford with a GUI similar
to that of a video game console. Although the latest
version 6.0 was released in 2012, it is still considered
in production.

-
Domain/OS:
Domain/OS was the proprietary OS for the defunct line
of Apollo/Domain workstations built with the like Motorola
M68k and PRISM (RISC) processors written in Pascal rather
than C or assembler (1981-92). This OS borrowed a lot of
its technology from System V and BSD. Domain/OS,
Apollo/Domain and related technologies were bought by HP.
Domain/OS was eventually replaced by HP-UX.

-
EmuTOS:
EmuTOS
is a replacement for Atari TOS with GEM as its GUI for
M68k or ColdFire chipsets that started in 2001. EmuTOS
comes from open
source "code from Digital Research, while
other parts have been developed from scratch... [with] no
code written by Atari in EmuTOS... distributed under the
GNU General Public License, version 2 (GPLv2)"
(Nov. 2019).

-
FreeRTOS:
FreeRTOS is a
real-time operating system (RTOS) for microcontrollers
that only needs 9 KB of RAM. As with most RTOS
configurations, FreeRTOS can operate with the Robot Operating System
(ROS) or any similar OS.
FreeRTOS is open
source and under the stewardship of (not owned by)
Amazon Web Services for its IoT services.

-
Graphic Environment Operating System:
There are two versions of GEOS developed by
Berkeley Softworks (later GeoWorks, now Breadbox), both of
which were propietary upon their original release and as
of 2014 open source. The original
version of GEOS
(8-bit) was released in 1986 as a replacement to KERNAL
(the original OS for C64 and C128) as well as other MOS
Technology 6502 computers and even the Apple IIe. The
latter might be the reason why the GEOS GUI resembled macOS 5.x.

The x86 16-bit version (PC/GEOS) was released
in 1990 as a Windows 95
replacement for older PCs and it is still supported. Since
becoming open
source, it has been referred to as FreeGEOS and
marketed as a shell for DOS. This
might be beneficial to promote FreeDOS instead of using the older and less
attractive FreeGEM 3.2.3
(2005).

-
GNU Hurd:
GNU
Hurd developed by the GNU Project is a microkernel to replace the Unix kernel and it is based on GNU Mach,
the same microkernel used by macOS/Darwin. The GNU Hurd microkernel can also be used to replace
the Linux kernel. As such, the GNU Hurd
project is to create a "general-purpose kernel
suitable for the GNU operating system" (Nov.
2020) that can also be used in other Unix-like
systems for full compliance between
systems.

-
Kano OS:
Kano OS
is the original OS for the Kano computer systems (2013)
— a series of hardware kits marketed primarily to
children to teach them how to build and configure
computers and laptops using modules with the parts needed
like Lego bricks. The OS is based on Raspbian
— a Debian distro tailored
for Rasberry Pi hardware and related peripherals. In other
words, Kano OS is Raspbian with educational
software including block programming. Note that on
December 2019, Kano replaced Kano OS in favor of Windows 10, which includes a
custom version of Minecraft (Mojang, purchased by
Microsoft) for children to hack. I understand that the
company needs to sell the product regarless how
educational it is, but siding with Microsoft for sales
intead of an open
source solution is a mistake.

-
KolibriOS:
KolibriOS is an x86
16/32-bit OS — forked from MenuetOS, written in FASM
(flat assembler) — heavily scaled down in order to
use low resources. As such, the 1.41 MB image
(.IMG) fits in a 1.44 MB floppy, that can be
burned to floppy or mounted as a virtual drive. The full
image available in an .ISO is under 70 MB and it
also needs at least 8 MB of RAM to load the OS. In either
case, the whole OS (not only the kernel) is loaded to
memory and not from disk to memory (no swapping). There is
no installation and any change you make can be written
back to the image — not to root (/), but
rather to one of the subdirectories in the image. One idea
is /fd/1/SETTINGS/RAMDRIVE.BAK to keep all OS
settings together and hence organized. The software
bundled in the image is interesting to say the least. Its
web browser WebView 2.65b is similar to Lynx, but with a
modern GUI. KolibriOS also has its own Bash-like shell
although limited to 28 external commands (excluding kernel
commands). The image comes with several games, several
emulators for several video game platforms like SNES and
even DOSBox. It seems like an excellent OS for
gaming although the it also includes several office,
programming languages like TinyBASIC and FASM (flat assembler) as well
as network utilities almost rivaling any Linux distribution.

-
MenuetOS is an x86 16/32-bit OS written in FASM (flat
assembler) and fits in a floppy. It needs a mouse,
i386, 32 MB of RAM and 1 MB Display Vesa 2.0+ LFB. I have
not had a chance to test MenuetOS although I have played a
lot with its fork KolibriOS. Note that the development of
MenuetOS seems to be on hold without any notice of
restarting soon, but not abandoned.

-
MichalOS:
MichalOS by Michal Prochazka is an
x86 16-bit open
source fork of MikeOS with a desktop
environment instead of a menu in the middle of the screen.
MichalOS has a nicer interface that asks for the user
enter a name and password for security writing data back
to its 1.8 MB image when written to a disk (not the 1.8 MB
read-only .ISO). If using the 1.41 MB floppy
image, there are parts of the OS missing like the used
and password set-up that I mentioned before. Since
MichalOS is forked from a previous version of MikeOS, 4.5
rather than the newest, the fork has the opportunity to
become its own OS.

-
MikeOS:
MikeOS
is an x86 16-bit open
source OS written in Netwide Assembler (NASM) by Mike
Saunders and others. This OS (currently 4.6.1) has low
system requirements — i386, keyboard, no mouse and 1
MB of RAM — and it runs from its floppy
image. The OS will a menu listing a set of files
including some programs you can run as with any OS. Note
that some of these files are not accessible as in the case
of KERNEL.BIN since it is a system file. What I
do not understand is why the file is not hidden in the
first place. Part of the idea behind MikeOS is teaching
how simple a 16-bit OS works with lots of documentation to
study and learn from. The MikeOS website has a collection
of applications for download including a package for mouse
support (MOUSE.LIB), BASIC
and C applications. Saunders seems to be doing something
right when his OS is getting forked. The most promising
fork is MichalOS by Michal Prochazka, which
according to the MikeOS website, already comes with mouse
support.

-
MINIX:
MINIX is an open source Unix-like OS written in C by Andrew
Tanenbaum (ast) of the
Vrije Universiteit Amsterdam in order to teach his
students how an OS works. MINIX is the OS that Linus
Torvalds used as the base of Linux.
MINIX supports various hardware configurations with minor
changes on the kernel or installing it from its source
code. Note that MINIX does not come with a GUI hence fully
CLI.

-
Möbius:
Möbius is an x86 16/32-bit open source OS that comes
in a floppy image set "out to be an
innovative new operating system while retaining
compatibility with and Win32" (Sep.
2013). When testing
Möbius, I ran into several errors and ended
contacting the developers. It seems that newer hardware
triggers kernel exceptions. I contacted the developer who
is looking into the errors.

-
MorphOS:
MorphOS is an OS
compatible with AmigaOS with a combination of
open source and
proprietary code, especially its kernel. It seems to be
marketed as a replacement for macOS on
hardware made in the past decade or so.

-
NewOS:
NewOS is an OS that is
under development written in C, C++ and assembler. This OS
can fit on a floppy. As per the developers, it is
"mostly a kernel with a minimal amount of user
space libraries and applications." This means
plain CLI, no GUI. If you want to try it, you can run its
binaries (located at /usr/local/i386-newos/bin)
on FreeBSD, Linux, macOS X or
Windows using Unix.
-
NitrOS-9:
NitrOS-9 is a "a real-time,
process-based, multitasking, multi-user, Unix-like operating system for Tandy CoCo, Dragon, and several
other Motorola MC6809-based computers" (Jun.
2017). NitrOS-9 is based on Microware OS-9.
![By Lamune (Talk) - Copyed from English Wikipedia
Tandycoco2.jpg], Copyrighted free use,
https://commons.wikimedia.org/w/index.php?curid=460962 By
Lamune (Talk) - Copyed from English Wikipedia
Tandycoco2.jpg], Copyrighted free use,
https://commons.wikimedia.org/w/index.php?curid=460962](/img/320px-TRS-80_Color_Computer_2-64K.jpg)
-
Public Domain OS (PDOS)
PDOS is a public domain (no ownership, no charge, no license)
16/32-bit x86 OS. Note that the DOS part of the
name is not for Disk
Operating System although PDOS can manage disks. The
only downside is that some commands have still not been
implemented like FORMAT or a macro similar to
DOSKEY. It still boasts 31 internal commands with
similar names as versions of DOS to flatten any learning curve.
-
ATTRIB
-
CD
-
CLS
-
COPY
-
DATE
-
DEL
-
DIR
-
ECHO
-
EXIT
-
GOTO
-
HELP
-
MCD — MD + CD
-
MD
-
OPTION
-
PATH
-
PAUSE
-
PEEK
-
POWEROFF
-
PROMPT
-
PS — processes running
-
RD
-
REBOOT
-
REM
-
REN
-
SAVE
-
SET
-
SLEEP
-
TIME
-
UNBOOT — marks a disk as non-bootable
-
V — video control
-
VER
It also includes five external commands, four of which
seem to do the same job.
-
EMACS.EXE
-
PDPTEST.EXE
-
PDPTESTA.EXE
-
PDPTESTV.EXE
-
PDPTESTW.EXE
-
Phantom OS:
Phantom OS is an
real-time operating system (RTOS) running from VM loaded
to RAM. The selling point of the OS is that it constantly
saves a snapshot of what it is doing. It achieves this by
paging a content in RAM "to disk in a way that
lets OS to restore whole memory image on
restart" (Nov. 2020). This way in the case of
power failure the machine can pick up where it left
off.

-
RIOT:
RIOT is a low-power IoT OS
that can also control microcontrollers. The product
website does not have much information. Perhaps the
developer expect users to know about the OS and what to do
with it.
-
RISC OS:
RISC OS takes its name
from "reduced instruction set computer
architecture" and was originally designed for by
Acorn Computers Ltd in Cambridge, England, released in
1987. Nowadays it is used in single-board computers like
the Raspberry Pi. There is an open source version available from RISC OS Open
Limited (ROOL).

-
SkyOS:
SkyOS is a mostly -complaint, but proprietary, OS "built
from scratch" by Robert Szeleney from 1997 to
2009. This Unix-like OS used a file
system forked from Be File System (BFS) named SkyFS (FS for file
system, of course).

-
Sortix:
Sortix is a self-hosting (lots of
emphasis on the latter) x86 32/64-bit free OS written by Dannish programer Jonas
"Sortie" Termansen. Sortix is not quite open source although
openly accessible as per its ISC license. The OS is -complaint. Although Sortix is not a Linux derivative, it has a lot of
similarities possibly to establish the
compatibility. As such, the learning curb is minimal if
your background is in Linux consoles.
-
Syllable:
Syllable was a mostly -complaint OS forked from AtheOS (an AmigaOS clone) in 2002. It needed at least an
i586 (60 MHz) and 32 MB of RAM. Syllable recommends at 128
MB for web surfing and I really doubt the minimum speed of
60 MHz of an i586 will work. Syllable used the AtheOS File
System (AFS), which was copied after the Be File System (BFS)
— in other words, partially cloned from BeOS, but not like Haiku. Note that both
AtheOS and Syllable shared the same domain name and seemed
to be part of the same project or at least related
projects inspired in BeOS technologies other
than just its file system. I tested Syllable 0.6.7
released on January 2010, which had a similar look and
feel of Haiku and
therefore BeOS. Syllable also
included Bash and has a similar directory structure as Linux with /atheos instead of
/root — different from BeOS.

-
Symbian:
Symbian was a mobile phone and real-time operating
system (RTOS) from 1998 to 2013. This OS started as EPOC
developed by Psion for their personal digital organizer
(PDA). Most Symbian applications were written using the Qt
framework, C, C++, Python, Java, Flash Lite, Ruby, .NET,
web runtime (based on ActiveX) and WebKit for the built-in
Opera web browser. In my opinion, the programming
languages used in this OS make it too close to Windows and its unliable
related technologies. In other words, Symbian looked on
paper like an unreliable OS.

-
TempleOS:
TempleOS (public
domain) is one of the strangest and possibly one of the
less visually appealing OSs ever created. This OS was
written by Terry Davis (1969-2018), who had been diagnosed
with mental illness and who was sure that God had asked
him to write this OS in a special version of C, which
Davis named Holy-C, and assembler. Using the OS is
difficult unless you understand its syntax — a
cross between C and C++ (C+).

-
Visopsys:
Visopsys (VISual
OPerating SYStem), created by Andrew McLaughlin in 2001
"from scratch", is an x86 32-bit Windows replacement with
read-only support for ext2 and ext3 used
by Linux and other Unix
clones. The latest version is 0.9 (32 MB .ISO)
released on April 2020. As with most OSs on this list, the
minimum requirements are low. It needs an i586 and 64 MB
of RAM to barely run. Of course, as with any other OS or
software, you need much more if you do not want
frustration to get the best of you.

-
VxWorks:
VxWorks
is a real-time operating system (RTOS), first released in
1987. It is not used in end-user applications, but rather
for scientific applications like autonomous robots. Two of
its most famous customers are Asimo by Honda
and the Mars Curiosity Rover.
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-
Xinu:
Xinu (Xinu is not Unix) is an
x86 open source OS written in
C — just like Unix — that needs to
be compiled from source (no image). It is promoted as not
being Unix. Functions and naming conventions
are similar to that of Unix, but the developing
team indicates that the source is different. I will try
testing this OS if the ftp.cs.purdue.edu server
goes online again in order to download the pre-built
VDI.
-
yuuOS:
yuuOS is
an x86 32-bit open
source OS written in C — not assembler as most
OSs in this list — by João Costa (a.k.a.
YuukiDesu9 or simply Yuuki) that runs
from its floppy-sized image — no installation.
Since Costa is the lead and practically sole programmer,
the development of this hobby OS is a tad slow. yuuOS
reminds of BOS — also on this list — with its
menu at the top prompting users to type the commands at
the bottom of the screen without any means to recall the
previous commands like DOSKEY.EXE.
